<p>The volume part is not always easy. Calculus II - 1/4 also does volume. It’s one of the hardest topics. Then you also have conics, polar, etc. People don’t do well in II only because there’s so much to remember.</p>
<p>Differential is not very difficult. If you do enough problems (provided that you have a good teacher and a good textbook…), it is a matter of mechanics. There are many tricks, but like I said - it’s all about mechanics. According to my professor, differential equation is just about tricks…</p>